A means of controlling a rotor of a helicopter utilizes cyclic pitch changes to its rotor blades. In this means, the control system changes the pitch of each helicopter rotor blade about its feathering axis once per rotor evolution. This is accomplished with a cyclic control stick. It is this stick, like the steering wheel of an automobile, that is in the pilot's way when he is thrown foward and downward in a crash.
With the adaptation of ejection seats for use in helicopters the cyclic stick became a matter of concern lest the stick strike the pilot as the pilot and his seat were leaving the aircraft and the cyclic stick remained in place. To overcome this danger, helicopters were designed with separable cyclic sticks held in place by restraining pins. Pin pullers were pyrotechnically actuated as an event of the seat ejection system.
Cyclic sticks have also been a matter of concern in crashing situations other than those involving ejection seats. Crashworthy helicopter seats which stroke downward upon impact increase rather than eliminate the danger of a pilot's chest, head or face striking the control stick of a helicopter. Carnell, et al., U.S. Pat. No. 4,655,416 describes and illustrates a prior art embodiment of a cyclic stick hinged so that it can be pulled out of the way of a pilot thrown forward and down by the impact of the crashing aircraft by a lanyard actuated by the movement of the stroking pilot's seat. In that disclosure we find a pyrotechnically energized cyclic stick repositioner, actuated by downward movement of the seat, as a means for dealing with this unresolved problem. Those means require mechanisms including pulleys and lanyards and may include a time delay before actuation. Hence, there is a need for an improved crashworthy cyclic control stick of the type provided herein.
Concerns analogous to those described above in conjunction with cyclic sticks have been reflected in automobile designs. A feature of safety automobile steering gear is the energy absorbing means provided by a steering column which yields or collapses on impact to mitigate head and chest injuries. This art is exemplified by Franchini, U.S. Pat. No. 3,556,550. The energy absorbing means in such steering gear mitigate, but do not eliminate, injuries in collisions.
The helicopter separable cyclic sticks described above have similar disadvantages. The automobile steering gear of U.S. Pat. No. 3,556,550 does yield when struck with sufficient force by the driver's body, but that technology is not translatable to helicopter control stick impact prevention because the steering gear travels a limited distance when it yields to impact, and has such inertial mass that driver injuries can only be mitigated and not prevented. A crashworthy cyclic control stick which is pilot actuated can overcome these disadvantages and is provided herein.